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首页> 外文期刊>Geochemistry, geophysics, geosystems >Early Miocene subduction in the western Mediterranean: Constraints from Rb-Sr multimineral isochron geochronology
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Early Miocene subduction in the western Mediterranean: Constraints from Rb-Sr multimineral isochron geochronology

机译：地中海西部中新世早期俯冲：Rb-Sr多矿物等时线年代学的约束

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摘要

The Betic Cordillera of southern Spain is a complex orogen formed in the context of convergence between Africa and Iberia from the Mesozoic to the present. The internal zone of the orogen includes three tectonic complexes, two of which have been subducted to high-pressure conditions, then exhumed back to the surface during subsequent extension. Subduction in the structurally lower complex, known as the Nevado-Filabride Complex (NFC), has been a topic of debate for several years due to conflicting geochronological data. Here we use multimineral isochron Rb-87/Sr-86 dating on carefully selected mineral samples from high-pressure metamorphic rocks in the NFC to better constrain the timing of high-pressure metamorphism and subduction in the region. Out of five samples analyzed, statistically valid multimineral isochrons were obtained for one eclogite and two schists, yielding ages of 20.11.1, 16.00.3, and 13.31.3 Ma, respectively. Despite that the other two eclogite samples appeared to preserve prograde mineral assemblages, low Rb-87/Sr-86 ratios in white mica precluded precise age calculations. These new ages are in close agreement with previously published Lu-Hf ages on garnet and U-Pb ages on metamorphic zircon overgrowths for the same rocks, but are substantially younger than published data from the Ar-40/Ar-39 technique. Combined with recently published tomographic images of slab structure beneath the Alboran Sea, the new ages support a tectonic model in which subduction occurred both prior to the Miocene and during the early to mid-Miocene, but that it was punctuated in time by a pulse of extensional exhumation in the early Miocene associated with lithospheric delamination and/or slab tearing.
机译：西班牙南部的比迪克山脉是从中生代到现在非洲和伊比利亚之间交汇的背景下形成的复杂造山带。造山带的内部区域包括三个构造复合体，其中两个已经俯冲到高压条件下，然后在随后的扩展中被发掘回地面。由于地球年代学数据的矛盾，在结构上较低的复合体（即内华达－费拉布赖德复合体（NFC））中的俯冲已成为争论的话题。在这里，我们使用NFC高压变质岩中精心挑选的矿物样品上的多矿物等时Rb-87 / Sr-86日期，以更好地约束该地区高压变质和俯冲的时间。在分析的五种样品中，获得了一个有效的榴辉岩和两个片岩的多矿物等时线，分别为20.11.1、16.00.3和13.31.3 Ma。尽管其他两个榴辉岩样品似乎保留了高级矿物组合，但白云母中低的Rb-87 / Sr-86比率妨碍了精确的年龄计算。这些新年龄与先前发表的相同岩石的石榴石石榴石Lu-Hf年龄和变质锆石过度生长的U-Pb年龄相吻合，但比Ar-40 / Ar-39技术发表的数据年轻得多。结合最近发布的Alboran海下面板状结构的断层图像，新时代支持了构造模型，其中俯冲发生在中新世之前和中新世早期至中期，但随着时间的推移，它被及时打断。中新世早期的扩张性发掘与岩石圈分层和/或平板撕裂有关。

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